This invention relates to a pulse control circuit and more particularly a pulse control circuit wherein the period between pulses can be varied continuously to drive a load, for example, a stepping motor.
FIG. 1 is a block diagram of one example of a prior art pulse control circuit adapted to drive a stepping motor utilized in an electronic computer. As shown in FIG. 1, the pulse control circuit 1 is comprised by a data table 2 from which information obtained from an electronic computer, not shown, or other source of speed controlling information, is derived. A register 11 is connected to receive a selected speed data signal count derived from data table 2 through a gate circuit 4 associated with a memory buffer circuit 3. An up-counter 14 is preset by the count signal obtained from the register 11 through a gate circuit 12 and is counted up by serially supplied input pulses obtained from a pulse generator 13. A detector 15 is responsive to an overflow output signal from the counter 14 for sending a signal to a stepping motor to be controlled, not shown, and also back to the gate circuit 12.
The pulse control circuit shown in FIG. 1 operates as follows. In response to a command signal from the electronic computer, one of the speed data values stored in the data table 2, is selected and its digital data value temporarily stored in memory buffer circuit 3. Upon application of a gate signal to the gate circuit 4 the value is transferred from memory buffer circuit 3 and stored in the register 11 which resets counter 14 each time gate 12 is activated. The pulses from the pulse generator 13 are applied serially to a second input of the counter 14. Each time the counter overflows, an output pulse signal is produced which is used as the speed control signal for application to the stepping motor (not shown). The output pulse also is fed back and applied to gate circuit 12 for enabling the resetting of counter 14 in accordance with the speed data then stored in register 11. So long as the data stored in the register 11 is not changed, the counter 14 produces a pulse signal having a period corresponding to the speed data count derived from data table 2 and stored in the register 11 and this pulse signal is applied to the stepping motor as the speed data pulse for driving the motor at a speed corresponding thereto.
With this prior art construction, although it is possible to vary the period or repetition rate of the pulses produced by the control circuit 1 in accordance with the speed data stored in the data table 2, the adjustment of the repetition rate must be accomplished by changing the value of the data stored in the data table 2. For this reason, when it is desired to provide a fine speed control or to vary the speed of the stepping motor over a wide range, it is necessary to revise the data stored in the data table 2. To this end, it is necessary not only to provide a special circuit for changing the data stored in the data table but also to change the information of the related circuits controlled by the data table. As has been pointed out hereinabove, the prior art pulse control circuit thus has problems with controlling the speed of the stepping motor finely and covering a wide range. Because of this characteristic, it is difficult to perform a simulation operation wherein it is necessary to continuously regulate the speed of a stepping motor while the operator observes the data which is produced as the stepping motor rotates and is displayed by a display device.